The present invention relates to concrete laying techniques, and more particularly to methods of erecting mass concrete structures.
The invention is applicable to civil engineering and can be used for the erection of different structures on frost-heaving ground and in permafrost areas.
According to the prior-art practice of erecting mass concrete structures on frost-heaving ground, the ground bed was warmed up before laying the concrete mix. In permafrost areas, concreting was preceded by preparing an insulating cushion of sand, gravel-and-sand mixture, crushed stone, and prefabricated or reinforced concrete.
In the Far North, where permafrost prevails, pile-supported structures have been increasingly common in recent years.
It must be pointed out, however, that the known techniques of erecting mass concrete structures on frost-heaving ground and in permafrost areas do not envisage the use of natural ground beds or foundations, whereby the cost of preparing such beds or foundations may be reduced to a minimum.
For example, in order to lay concrete on a frost-heaving bed, the latter must be warmed up, which is a labor- and power-consuming process. Moreover, this method does not always work, especially at low ambient temperatures and when the ground is frozen to a great depth.
Prior to laying concrete in permafrost areas, an insulating cushion has to be provided on the ground bed. The cushion consists of sand, sand-and-gravel mixture, crushed stone, and prefabricated and reinforced concrete.
Yet this type of insulation does not completely rule out the penetration of free moisture from the concrete mix through the insulating material into the ground bed. As a result, the permafrost thaws, and the supporting capacity of the ground is sharply reduced.
The known method has another disadvantage which is still more important. The method does not ensure a wholly monolithic structure, which, in turn, results in a non-uniform load distribution and strain cracking. The consequences may be disastrous.
Pile-supported structures, although highly durable, are quite costly. Besides, this technical solution does not ensure a monolithic structure which is an absolute necessity in a number of cases. There are also cases when this technique proves to be impracticable both technically and economically. A case in point is a covering extending over a great distance, for example, an airfield or road pavements.